In a pump apparatus, in order to make the pump apparatus lightweight and lower manufacturing cost of the pump apparatus, it has been practiced to form a pump casing by assembling pressed products which are manufactured by press-forming of sheet metal such as stainless steel plate, and then to amount this pump casing on a flange of a motor.
Conventionally, in this kind of pump apparatus, as shown in FIG. 7, a pump casing (pressed pump casing) 10 composed of pressed products is prepared, and bolts 14 are fixed by welding or the like to a backside plate 12 of the pump casing 10 at predetermined positions on the circumference in a peripheral portion of the backside plate 12 such that shaft portions of the bolts 14 project from the backside plate 12 backwardly. Next, the shaft portions of thee bolts 14 are passed through through-holes 16a formed in a flange 16 of a motor, and the backside plate 12 is brought into contact with the flange 16 at the peripheral portion of the backside plate 12, and then nuts 18 are screwed onto the bolts 14 to fasten the backside plate 12 and the flange 16 together, thereby mounting the pump casing 10 onto the motor. This fastening method is also used for fastening another member to a plate having a complicate shape.
However, the work for fixing bolts to a plate having a complicate shape by welding or the like is inefficient, and is the major factor in causing an increase in production costs. Particularly, in the pump casing (pressed pump casing) composed of the pressed products manufactured by press-forming of sheet metal such as stainless steel plate, many welding operations and many components are necessary, and hence the working efficiency is extremely low. Although the pressed pump casing has been proposed for reduction of production costs, such pressed pump results in an increase in production costs all the more because of the above reason.